FR2579912A1 - - Google Patents

Abstract

A method and apparatus for bending thick metal tubes is disclosed and is characterized in that thermal insulation is disposed inside the heated zone of the tube being bent, and that the thickness of said thermal insulation is great enough to considerably reduce the temperature gradient between the inside and outside surfaces of the tube in said heated zone.

Description

Method of bending a thick metal tube, and device for its implementation

  The present invention relates to a method of bending a thick metal tube of constant cross-section, by localized heating of a narrow zone around the periphery of this tube by means of a heating collar surrounding this zone, pushed on a end of the tube and maintaining

  its other end by a pivoting arm, in which

  the temperature of the heated zone around the perimeter of the

  by detecting the temperature of the latter OR the separate air gap

  the heating collar of the periphery of this zone, in at least two points of this periphery, one of which is on the side of the center of curvature, and

  the other opposite to the first, and by increasing or decreasing the heat supply.

  to one or other of these points depending on whether the temperature is lower or higher, or whether the air gap is greater or less, than a reference value corresponding to a temperature

  uniform, one has a uniform air gap, around the heated area.

  It also extends to a device for implementing this method.

  It has already been proposed in the patent application FR-A-2 488 162 of the Applicant a method of this kind, applicable more generally

  to any elongated metallic element of constant cross section.

  However, it has been found in the implementation of such a method for thick tubes that there appears to be a significant temperature gradient between the external surface of the heated zone and its internal surface. In the usual case where the heating collar is an inductive element generating eddy currents in the tube, only the first 15 to 20 mm of the thickness of the tube from its external surface are heated by the eddy currents, the rest the thickness being heated only by conduction and therefore remaining at a lower temperature. This high temperature gradient results in a relatively high average coefficient of plasticity stress. If one wants to avoid the appearance of defects on the inner surface of the tube, this therefore requires a relatively slow advance of the tube to be bent, and consequently a hourly production of tube bent lower than what can be achieved with tubes sufficiently thin so that the temperature of the heated zone remains substantially constant over the entire thickness of the

2579912-

  -2 - tube. This difficulty is particularly important, for example with the low-alloy steel tubes containing 2-2.5% by weight of chromium and 0.9-1.2% by weight of molybdenum of the so-called CD 9.10 grade (designation

DIN 10 Cr Mo 9.10).

  The object of the present invention is to provide a method and a device for bending a thick metal tube which reduces to a relatively small value the temperature gradient between the external and internal surfaces of the heated zone, which ensures good behavior control. of the tube to be bent, and correlatively decreases the average coefficient of plasticity stress of this zone, and

  As a result, a larger hourly production of curved tubes.

  The process according to the invention is characterized in that

  placing a heat insulation inside the heated zone in a sufficient thickness to significantly reduce the temperature gradient

  between the outer and inner surfaces of the tube in the heated zone.

  The device according to the invention is characterized in that it comprises a cylindrical carriage with internal guide rollers of the tube,

  to which is fixed downstream in the direction of advance of the tube a metal ring

  that support covered with a heat insulating layer of outer diameter close to the internal diameter of the tube, and held by a fixed rod in a position such that the insulation layer is at the heated zone. Hereinafter, by way of example and with reference to the figures of the accompanying drawings, a device for bending a metal tube is described below.

thick according to the invention.

  Figure 1 shows the entire bending device.

  Figure 2 shows on an enlarged scale the detail 16 of the

figure 1.

  The invention is more particularly applicable to low-alloy steel tubes containing 2-2.5% by weight of chromium and 0.9-1.2% by weight of molybdenum, in particular those corresponding to the so-called 10 CD 9.10 grade ( DIN 10 Cr Mo 9 10), whose metallurgical behavior and the coefficient

  Plasticity stress varies a lot with temperature.

  The thick tube to be bent 1 undergoes a longitudinal thrust exerted by the shoe 2. At its other end, an arm 3 pivoting about an axis 4 and enclosing the tube in a jaw 5 ensures the bending of the tube, worn locally. at a high temperature by an inductor collar 6. A diabolo 7 guides the tube externally upstream and close to the zone

heated by the heating collar.

  Inside the tube, a carriage 8 is held by a rod 9 connected to a fixed point 10 at a constant distance from this fixed point. This carriage is provided with guide rollers 11, 12, 13. It is connected to this carriage 8 opposite the rod a support ring 14 provided on its periphery with a layer 15 of heat insulation such as rockwool. The

  distance D between the point of attachment 10 of the rod 9 and the plane of symmetry

  the heated area (or insulation) must be kept constant. The support ring 14 is formed for example of four sectors of

    connecting to each other by means of cover plates.

  On its cheeks 17, 18 secured by a spacer 19, are fixed flanges 20, 21 supporting the rollers 11, 12. A bracket 22 carries a rod 23 for supporting a flange 24 carrying the roller 13. The flange 24

  is pushed by a helical spring 25 towards the inner wall of the tube.

  The zone heated to a temperature such that the plasticity stress is exceeded being located a little downstream of the heating collar in the direction of advance of the tube, the heat insulation 15 decreases the gradient of

  temperature through the thickness of the tube, and thus ensures a coeffi-

  This means of plasticity constraint of the tube greater than that which would be obtained in the absence of heat insulation. It thus makes it possible to increase the advance speed of the tube and the hourly production of bent tube, and correspondingly makes it possible to increase the capacity in diameter and thickness.

  bendable tubes on the machine.

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Claims (2)

  1 / A method of bending a thick metal tube of constant cross-section (1) by localized heating of a narrow zone of the periphery of this tube by means of a heating collar (6) surrounding this zone, pushed on a end of the tube and maintaining its other end by a pivoting arm (3), in which the temperature of the heated zone is kept substantially constant around the perimeter of the tube by detecting the   temperature of the latter or the air gap separating the heating collar.   the periphery of this zone, in at least two points of this periphery, one of which is on the side of the center of curvature, and the other opposite to the first, and increasing or decreasing the thermal contribution in one or the other of these points, depending on whether the temperature is lower or higher, or whether the air gap is greater or less, than a reference value corresponding to a uniform temperature, or to a uniform air gap, around the heated zone. , characterized in that inside the heated zone a   insulation (15) in a thickness sufficient to reduce noticeably   the temperature gradient between the outer and inner surfaces of the tube in the heated area.   2 / Apparatus for implementing the method according to claim 1, characterized in that it comprises a cylindrical carriage (8) with rollers (11, 12, 13) of internal guide tube, which is connected downstream with respect to the direction of advance of the tube, a metal support ring (14) covered with a heat insulating layer (15) of external diameter close to the internal diameter of the tube, and held by a fixed rod (9) in a position such that the layer insulation is at the level of the zone heated tube.